The present invention relates to fluid operated systems using liquids as the working fluids in those systems such as hydraulic forcing systems and engine lubricating systems and, more particularly, to gas turbine engines such as turbofan engines and associated integrated drive generator lubrication systems.
Lubrication systems for turbine engines, such as a turbofan engine, and for associated equipment, such as an integrated drive generator, provide pressurized lubricant, an oil, to lubricate, cool and clean the engine main bearings, gear box gears, seals, and the like, and again for the lubrication of bearings and other parts in equipment associated with such turbine engines. During such lubrications, leakages past seals, and heating of the lubricating oil caused to occur due to mechanical energy losses in the lubricated apparatus that leads to evaporation, together result in lubricating oil losses during engine operations.
Such losses, even with a lubrication system oil reservoir, or reservoirs, for storing additional oil being continually kept available to the system, must be countered by adding further replacement oil at appropriate times to that reservoir or reservoirs. Thus, the remaining volume of the oil in the lubricating system after use of the corresponding engine or other equipment lubricated by the system is required to be monitored to determine the times at which additional oil must be added to the reservoir. Similarly, losses of hydraulic fluid, or leaks into the system, occur during operations of hydraulic systems thus also requiring the monitoring of the remaining volume of hydraulic fluid as the basis for replenishing same as needed.
Although seemingly such monitoring can be accomplished by simply noting the level of oil or hydraulic fluid in the corresponding reservoir, thermal expansion of the lubricating oil or fluid due to the heating thereof causes significant variations in the levels thereof at different temperatures as those levels are measured in those reservoir or reservoirs for a given actual mass of such oil or fluid in the system because the volume of that oil or fluid depends on its temperature. This dependence makes the determination difficult as to just what the current volume of oil is in a lubricating system by just measuring the volume in the reservoir, typically done through just measuring the depth of the oil therein. The same situation also typically arises in hydraulic systems. Thus, there is a desire to provide a method of accurately determining the current amount of a working fluid present in a working fluid operated system relative to the desired amount, i.e., for example, the amount of lubricating oil present in an turbofan engine lubricating system versus its initial fill amount, and to do so through a conveniently performed volume measurement which can be done at whatever the temperature is of that working fluid at the time of making that measurement.